1. Field of the Invention
The present invention relates to a composition for depigmenting or bleaching mammalian skin containing L-2-oxothiazolidine-4-carboxylic acid and at least one polyol.
2. Discussion of the Background
The color of mammalian skin, such as human, depends on many factors and, in particular, on the seasons of the year, race and sex, for example. It is, however, mainly determined by the concentration of melanin produced by melanocytes.
For several years attempts have been made to reduce and/or slow down production of melanin in order to depigment or bleach the skin, by acting on one or more of the intermediates produced in the intracellular biochemical synthesis of melanin. In this effort, different chemical entities have been tested and used as depigmenting or bleaching agents. In particular, compounds such as vitamin C, vitamin C derivatives or vitamin E derivatives, arbutin, hydroquinone, kojic acid, placenta derivatives and glutathione and derivatives thereof have been incorporated into compositions and tested.
The above compounds are known to act on the synthesis and/or activity of tyrosinase, an enzyme which plays a part in the synthesis of melanin, or are known to reduce the amount of melanin formed or, alternatively, are known to stimulate the removal of melanin via keratinocytes. Unfortunately, these compounds are either toxic when applied to the skin, in the case of hydroquinone, are unstable in solution, in the case of vitamin C and kojic acid, which complicates the manufacture of the composition, or have unpleasant odors, in particular, sulphurous odors, such as glutathione, which consequently limits the use thereof. Moreover, the above tyrosinase- or tyrosinase synthesis-inhibitors are very limited in number.
It is also known to use L-2-oxothiazolidine-4-carboxylic acid in cosmetic or dermatological compositions intended for topical application for prevention of hair loss or to stimulate the regrowth of hair, as described in EP-656,201.
However, procysteine has a certain level of instability, in particular when it is in the presence of water. Thus, when it is introduced into a cosmetic composition, in particular a composition containing water, its efficiency decreases over time. In addition, the composition into which it is introduced shows signs of degradation, i.e., coloration and odor, after a certain period of storage, which are, of course, unacceptable to users.
Thus, a need exists for a skin bleaching agent which is as effective in its action as those that are known but which avoids the above drawbacks, i.e., one which is stable in a composition, which is not toxic to the skin and which has no unpleasant odors, particularly upon application.
A need also exists for a composition which can be used in cosmetic and/or dermatological fields containing L-2-oxothiazolidine-4-carboxylic acid, the latter remaining stable over time.